As illustrated in FIG. 1, the existing pouch type lithium ion battery cell has a structure in which a pouch 5 covers a battery unit 4 in which a cathode 1, an anode 2, a separation membrane 3 are sequentially stacked and an electrolyte injects and seals the pouch 5.
As the existing battery cell is repeatedly charged and discharged, the electrolyte included therein is depleted and a reactant 6 is accumulated from both ends 7 in a longitudinal direction of the anode 2. This causes a volume expansion of both ends 7 in a longitudinal direction of the battery unit 4. The volume expansion of the battery unit 4 increases a distance between the electrodes to increase an internal resistance and accelerate a deterioration to reduce use efficiency of a battery cell.
Meanwhile, an exterior material of a pouch is configured of a thin film having a thickness of 150 μm and therefore has no rigidity to suppress the volume expansion occurring inside the battery cell. Therefore, the pouch does not stop the volume expansion of the battery unit. Further, as described above, the expansion of the battery unit increases the internal resistance at the time of charging and discharging to reduce the use efficiency of the battery cell and reduce endurance reliability of the battery cell.
Further, the existing pouch type lithium ion battery cell has the battery unit positioned in the pouch and the electrolyte injected into the pouch and is then vacuum-packaged to completely remove air inside the pouch. In this case, the pouch does not have rigidity and therefore may not maintain a form and therefore the remaining space other than the portion in which the battery unit is positioned is compressed in a vacuum state and the electrolyte may not be present.
Therefore, the existing pouch type lithium ion battery cell does not have an additional space in which the electrolyte may be present, except for the battery unit. Due to the structural limitation, as the charging and discharging are repeated, the electrolyte is depleted, and as a result, the deterioration in the battery cell to reduce the use efficiency of the battery occurs.